Sennheiser Amazon Price Jump?

So I was looking around on Amazon today when I saw that the Sennheiser HD 650s had bumped up from $350 to $478! And the 595s had also gone up in price a significant amount. Is there a reason for this? I don't get it. I sure hope the 650s go back down some time soon.

Amazon uses dynamic pricing which changes price based on stock, purchases, page visits and other factors. It's quite interesting but thanks to the pricing systems you'll also sometimes see massive drops in price (ex: I got a $199 acoustic guitar for $60) :D